Determination of the energetics of formation of semiconductor/dendrimer nanohybrid materials: implications on the size and size distribution of nanocrystals† Somrita Mondal, Debasmita Ghosh, Chandra Nath Roy and Abhijit Saha * The synthesis of inorganic–organic hybrid nanomaterials has attracted considerable interest in recent years because of their multifaceted applications, such as in optoelectronics, cellular imaging, drug delivery, etc. The maneuvering of controlling parameters is key to the successful fabrication of good quality materials. However, the fundamental aspects pertaining to the thermodynamics of growth of such nano hybrid materials has so far not been unraveled. Here, we have investigated the energetics behind the formation of semiconductor–dendrimer nanohybrid materials using isothermal calorimetry. It is apparent from the observed energy release profile that the heat change for the formation of nanoclusters in phase II saturates faster with an increase in starting materials or monomer concentrations. We have also shown variation of the thermodynamic parameters with changes in the synthesis conditions, such as temperature, dendrimer generation and dendrimer core or surface groups. Based on a bi-phasic thermogram and the dependence of thermodynamic parameters on the dendrimer core and surface functionalities, it is suggested that nanoparticles are formed inside dendrimer molecules in the initial time period and on the outer surface at a longer time scale. Furthermore, it is observed that the formation of quantum dot–dendrimer hybrid materials is an exothermic, spontaneous and enthalpy driven process. Also, a lower temperature thermodynamically favors formation in the core of dendrimer molecules leading to smaller particles with a narrower distribution. The observed results suggest that higher values of formation constant and enthalpy are likely to make dendrimers of higher generation better templates for the synthesis of nanoparticles. The dependence of the ratio of concentrations of reacting metal ions (Cd or Zn) to sulfide ions shows a differential size pattern for CdS and ZnS nanoparticles, which has been interpreted in terms of binding constants determined calorimetrically. It is shown that enthalpy–entropy compensation takes place in the synthesis process affording favorable free energy. Such investigation can provide useful guidelines for the synthesis of better quality semiconductor–dendrimer hybrid nanomaterials. Introduction Hybrid inorganic–organic core–shell nanoparticles (NPs) are nding a wide range of applications in solar cells, optoelec- tronics, nanophotonics/plasmonics, catalysis, drug delivery and biomedical imaging agents. Their chemical, electronic, optical, magnetic and catalytic properties, and self-assembly inherently depend on their size and composition. 1 In recent years, poly- amidoamines (PAMAM) dendrimer has gained considerable interest because of its unique structure and provides building blocks for growing metal or semiconductor nanostructures. 2,3 These highly branched macromolecules are known to be robust, covalently xed and its three dimensional structures possess both a solvent lled interior core which is well suited for host– guest interactions and the encapsulation of guest molecules (a nanoscale container) as well as a homogeneous, mathemat- ically dened exterior surface functionality (nano-scaffold). In addition, dendrimers exhibit biomimetic properties and low cytotoxicity which make them potentially useful for gene transfection and drug delivery. Thus, the amalgamation of the biomimetic properties of dendrimers with excellent lumines- cence properties of semiconductor NPs 4–6 like CdS, ZnS, CdTe etc., can lead to the fabrication of novel hybrid materials ideally suited for various biomedical applications, such as drug delivery, cellular imaging, etc. 7 Our research group has been developing one-pot non-injec- tion approaches to fabricate good quality Group II–VI quantum UGC-DAE Consortium for Scientic Research, Kolkata Centre, III/LB-8 Bidhannagar, Kolkata 700 098, India. E-mail: abhijit@alpha.iuc.res.in; Fax: +91-33-23357008; Tel: +91-33-23351866 † Electronic supplementary information (ESI) available: Optical characterization of the nanoparticles is presented in the ESI. See DOI: 10.1039/c3ra47960a Cite this: RSC Adv. , 2014, 4, 13085 Received 25th December 2013 Accepted 22nd January 2014 DOI: 10.1039/c3ra47960a www.rsc.org/advances This journal is © The Royal Society of Chemistry 2014 RSC Adv. , 2014, 4, 13085–13092 | 13085 RSC Advances PAPER Published on 24 January 2014. Downloaded by University of Massachusetts - Amherst on 30/04/2015 14:43:53. View Article Online View Journal | View Issue